Circuit breaker



B. P. BAKER 1,973,460

C IRCUIT BREAKER Sept.- 11, 1934.

Filed June 15, 1932 3 Sheets-Sheet l WITNESSES: v U INVENTOR Sept. 11, 1934.

B. P. BAKER 1,973,460

CIRCUIT BREAKER Filed June 15, 1932 3 Sheets-Sheet 2 3/ 22/19/4 @6 Q WITNESSES: INVligg lf/ Ben am/)7 a 6/? ATTORN Y 45. P. BAKER CIRCUIT BREAKER Sept. 11, 1934.

Filed June 15, 1932 3 Sheets-Sheet 5 S'facK Impedance INVENTOR Beg/007i) PEG/(e ATTORNEY Patented Sept. 11, 1934 CIRCUIT BREAKER Benjamin P. Baker, Turtle Creek, Pa., assignor to Westinghouse Electric '& Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 15, 1932, Serial No. 617,306

40 Claims.

My invention relates to circuit inter'rupters and particularly to are extinguishing structures therefor.

In the type of arc extinguisher to which my invention is particularly applicable, the arc is drawn within a vertical chamber-like structure of insulating material, which is usually immersed in a liquid and which contains spaced slotted plates of magnetic material insulated from each other and arranged substantially transverse to the arc path. These plates so distort the magnetic field set up about the arc that the arc is forced into passages within the structure where it is cooled and deionized by the out-fiowing gases.

The commercial form of this structure, as is shown in the drawings, is made by assembling similarly slotted insulated and magnetic plates into a stack.

One object of my invention is to so alter the overall electrical characteristics of such a structure that a controlled voltage gradient may be secured when normal charging current flows therethrough.

Another object of my invention is to prevent the formation of corona stresses in arc extinguishing structures having electrostatically floating conducting plates therein.

A further object of my invention is to provide a simple, practical means for inserting admittance between the conducting plates of an arc extinguishing structure.

A further object of my invention is to provide means for altering the specific dielectric constant and the dielectric strength of the insulation within an arc extinguishing structure in such places that flashover from the moving contactthrough the structure shall be obviated, and, at the same time, to avoid objectionable increases in the open circuit voltage gradient.

A still further object'of my invention is to provide an admittance path for interconnecting the arc extinguishing structures of a \r'nulti-break circuitinterrupter in such manner that the voltage of the controlled circuit shall be divided substantially equally therebetween during the operation of the device.

The are extinguishing structure to which my invention is particularly applicable comprises an assemblage of parts wherein plates of magnetic material are interposed between insulating plates, 1. e., floated electrostatically therebetween. When this structure is subjected to the operating voltage, it is found that a charging current flows therethrough. Furthermore, since there is ca:

pacitance between these electrostatically flowing plates and the adjacent metallic parts-tank, bridging bar, etc.--as well as between the plates themselves, the charging current is not of uniform density throughout the structure; rather, there is a leakage actionalong its entire length which results in an increasingly greater current density as the line terminal end of the extinguisher is approached. And, since the unit admittance of the stack is substantially constant, this unequal current density condition longitudinally along the structure results in an unequal voltage gradient directly proportional to the unequal distribution of current.

Three particular objectionable conditions arise as a result of this unequal voltage gradient. First, it necessitates a longer, less economical extinguisher structure, because, in order to keep the voltage gradient within safe limits at the top of the device, it is necessary to reduce the working potential of the lower portions of the device far below their maximum safe value. In fact, in a test of applicant's device it was found possible to raise the normal operating voltage of similarly dimensioned extinguishers about Second, this concentration of potential drop at the top of the extinguisher structure is conducive to corona formation which may reach sufllcient magnitude to permanently damage the stack insulation. Third, any improvement in the dielectric adjacent the contact point is precluded, because it further intensifies the unequal gradient.

A further disadvantage may arise from these electrostatically floating conducting plates; since the coupling therebetween is negligible, the circuit characteristics of the assembled arc extinguisher stack structure approaches that of a group of serially connected condensers, and it is possible on transmission lines of certain characteristics to set up high frequency oscillations which may cause serious line disturbances.

My invention provides admittance means for interconnecting the magnetic plates, and thereby provides a conducting path in parallel with the stack structure proper. By a proper proportioning of this admittance means the voltage gradient along the stack may be controlled so as to secure the most efiicient operation of the device and thus overcome the above mentioned difliculties.

The admittance of the current carrying means which provides a conducting path between the magnetic plates within the arc extinguishing structure is made large in comparison with the admittance of the path between those plates and the surrounding magnetic parts-tank, bridging bar, etc. Thus, the voltage gradient is pre-- vented from reaching an objectionable value at any place which would decrease the effectiveness of the breaker. Likewise, the elimination of high potential gradients along the structure prevents corona formation with the resulting reduction in' the stack to the tank breakdown voltage.

when a double break oil circuit breaker having a grounded metallic tank is being tested for circuit interruption from line to ground, it has been found that at the time current zero most of the restored voltage (in some cases appears across the break adjacent to the high tension side. Under these conditions, as has been shown by laboratory tests, a double break interrupter will give an interrupting performance almost as good with one arc shorted out as with the two arcs. By having an admittance path which connects the electrostatically floated plates with the line potential and by connecting the movable contact member through a sliding contact to each of these admittance paths, it is possible to cause the movable contact member to fioat electrostatically midway between the potential of the two terminals and thus cause each of the arc paths totake its share of the potential.

During the time of arc extinction when the power system is most likely to be thrown into electrostatic oscillation, this admittance path which connects the movable contact member with the line terminals is very effective in damping out oscillations and in preventing dangerous peak.

voltages at the beginning of the circuit transient. During the closing process, a point is reached where the dielectric between the contact tip of the moving contact member and the stationary contact is no longer able to withstand the impressed voltage, whereupon it breaks down. This is a characteristic of all circuit making devices. So long as the dielectric of the arc extinguisher stack structure in that region adjacent to the contact point has a higher resistance than the surrounding medium the operation is normal and no damage results. But if the resistance of that part of the stack should be decreased-due to deterioration or other'causes-to a lower value than that of the medium, the breakdown will take place through the extinguisher itself with con-' siderable damage thereto. My invention, how'- ever, permits the insertion of additional insulating means of highdielectric strength into the stack adjacent the stationary contact without causing objectionable local increases in the voltage gradient. Thus, the conductivity of the stack at this or similar points is adjusted so that breakdowns through the stack structure on closing are prevented; and a general increase in the efilciency, reliability and safety of the circuit interrupter is secured. a

In the above discussion of the theory of operation of my invention, I have indicated how my invention has solved the five major'problems of high voltage circuit breaker arc extinguisher designs, which are: One, the control of the-voltage gradient between the live parts of a circuit interrupter and the grounded parts-tank, mechanism, etc. Two, the control of the distribution of the open circuit charging currents, which is exactly the same problem as the control of the potential gradient along an arc extinguishing device. Three, the-control of the point of flashover when the circuit breaker is being closed with normal voltage across the contacts. Four, the control of transient conditions to prevent excessive peak voltage and prolonged oscillatory mvaeco disturbances following the interruption of cer-- tain types of circuits in which the constants are not well chosen. And five, the control of the division of voltage between the serially connected breaks of a multi-break circuit interrupter during the opening of the controlled circuit.

The features of the invention which I believe to be new are particularly pointed out in the appended claims. For a full understanding of these principles and the best mode of applying the same, reference may be had to the accompanying drawings, in which:

Figure 1 is a cross sectional view, partly in elevation, of an oil circuit breaker equipped with the plate type arc extinguishing structures previously described.

Fig. 2 is a reduced cross sectional view through one of the stack structures embodying my invention on the line II-II of Fig. 3; certain of the parts ,are shown in elevation to more clearlyillustrate the structural features involved.

Fig. 3 is an enlarged cross sectional view on the line III-III of Fig. 2. v

Fig. 4 and Fig.5 are enlarged plan and elevational views, respectively, of the sliding contact members shown in elevation in Figs. 1 and 2.

Fig. 6 is an enlarged cross sectional view on the line VI--VI of Fig. 2.

Figs. 7, 8, 9, 10, 11, and 12 are plan views of the various plates used in the arc extinguishing structure.

Fig. 13 is an enlarged perspective view of one of the graphite impregnated fullerboard resistance discs used in carrying out my invention.

Figs. 14 and 15 are enlarged cross sectional views corresponding to Fig. 6 which illustratetwo modifications of my invention.

Figs. 16, 17, and 18 are diagrammatic views showing the electrical characteristics of the type of circuit interrupters to which my invention is especially applicable, and

Fig. 19 is a curve illustratingthe variation of the stack flashover voltage with the overall stack resistance. i

In the carrying out of this particular embodiment of my invention, I employ the customary breaker structure of. a tank 1 having a cover 2, insulating lead-in bushings 3 extending therethrough, a body of liquid 4, stationary contacts 5, -a bridging bar 7 having contact tips 9, a pull rod 11 for moving the bridging bar, and mechanism (not shown) for actuating the pull rod.

Each of the stationary contacts 5 comprises a hinged contact member 15, biased downwardly by a spring 17, for engaging the cooperating contact tip 9. Shunts 19 and 20 connect the terminal of conductor 18 which extends through bushing 3 to the hinged contact 15 and the arcing horn 22 respectively.

The are extinguishing device .13, which is shown in cross section in Figs. 2, 3, and 6, cominsulating plates 27, shown in Fig. 8, each having the slots 34 and 35 and the openings 29, assembled on opposite sides of a magneticplate 32 anda lining plate 26, of insulating material, both last mentioned plates being shown in Fig.

10. The magnetic plates 32 contain a large open slot that is lined by the insulating plate 26 which contains slots 34 and 35 similar to slots 34 and 35 in plates 27. In addition to the above, each unit group includes a plurality of .insulating plates 28 (Fig. 11), of absorbent material such as fullerboard, which are assembled between the fiber plate-magnetic plate-fiber plate assemblage of the adjacent units. These insulating plates 28 all have the common slot 34, and along the sides of this slot, a plurality of recesses 36 are provided for retaining the arc extinguishing fluid. In addition, plates 28 have the slot 35 which is common to all the insulating plates of the structure, the openings 29, and flared openings 23. The flared openings 23 serve to form vents for the arc gases generated within the arc extinguishing structure during the extinguishment of the arc.

The lining plates 26 are employed, primarily to protect the inner edges of the magnetic plates 32 from the action of the arc.

At this point, I wish to direct particular attention to the means whereby I interconnect the electrostatically isolated iron plates 32 within the group assemblages. For accomplishing this, I prefer to use graphite impregnated fullerboard discs 31 having a specific resistance of approxi mately 10 to 10" ohms per cubic centimeter. This value of specific resistance, however, is not of primary importance since the desired change is the provision of an admittance path through the stack. These discs 31 are shown in the enlarged perspective view of Fig. 13. Before assembling the plate structure, I insert one of these discs in each of the openings 29 in the insulating plates 27 and 28. Since these openings 29 align throughout the entire assemblage, and since the projecting portions 22' of the arcing horn 22, which is electrically connected to the line terminal, conductively engages the top discs 31, it becomes apparent, at once, that by this construction I am able to form a continuous conductive path throughout the stack, with the magnetic plates 32 positively interconnected and thereby made to assume the desired potential.

The complete arc extinguishing assemblage 13 comprises a top insulating plate 21, as shown in Fig. 7, which is provided with an arcing horn 22 andthe slot 35 which permits the passage of the contact tip 9, a plurality of the previously described unit group assemblages, and a bottom insulating plate 33 which has the common slot 35, the opening 23, and the conducting plate 38 which is imbedded therein as shown in Fig. 12. The common slots 34 and 35, and the recesses 36 are aligned during the assembly of the various plate elements, and the resultant structure is a chamber having a groove or passage formed by the slots 35-wherein the contact tips move (and wherein the arc is drawn)insu lated magnetic plates arranged transverse to the arc path, vents along the groove which are formed by the flared openings 23, and an extension of this groove into the structure which is formed by the recesses 36 and the connecting slots 34. The cross section views of Figs. 2, 3, and 6 show, in detail, the relative positions of the various plates and the arrangement of the various interconnecting slots and recesses.

Two flexible contact members 40 of conducting material are provided for slidably connecting the contacttips 9 of the bridging bar '7 with the lower end of the stack of interconnected, superposed iron plates 32. One of these contact members 40 is fastened to each bottom plate 33 by a screw 41 which extends through a suitable opening 42 and engages the conducting plate 38. The conducting plate 38 is imbedded in the bottom plate 33 and has two portions 38' which conductively engage the discs 31. It is thus possible to connect the bridging bar 7-through the admittance path which forms a part of the arc extinguisher structurewith each of the line terminals. And, as has been pointed out previously, the connection assures a substantially equal division of voltage between the two breaks under the most adverse operating conditions.

Fig. 14, as mentioned before, is an enlarged cross sectional view, corresponding to Fig. 6, in which is shown a modification of my invention. Specifically, the overall electrical characterstic of the stack is altered in this modification by the introduction of both resistance and capacitance. The same elements shown in Figs. '7 to 12, inclusive, are employed, but these elements are combined into two difierent unit group assemblages, and the complete structure includes a pluarlity of each of these groups alternately disposed.

For the purpose of simplification, I shall designate these two unit group assemblages as group assemblage A and group assemblage B, and shall describe each in detail.

Group assemblage A is exactly the same assemblage as that used in the embodiment of my invention shown in Figs. 2, 3, and 6; it includes two fiber insulating plates 2'], shown in Fig. 8, each having the slots 34 and 35 and the openings 29, assembled on opposite sides of a magnetic plate 32 and a lining plate 26, both last mentioned plates beingshown in Fig. 10. The magnetic plate 32 contains a large open slot that is lined by the insulating plate 26 which contains the slots 34 and 35-similar to slots 34 and 35 in plates 27. In addition, each group assemblage A includes a plurality of insulating plates 28, shown in Fig. 11, assembled on the side of the fiber plate-magnetic plate-fiber plate assemblage adjacent the next group assemblage. These insulating plates 28 all have the common slot 34 along the sides of which a plurality of recesses 36 are provided for retaining the are extinguishing fluid. In addition, plates 28 have the slot 35-'which is common to all the insulating plates of the structure-the openings 29 and the openings 23. The openings 23 serve to form vents for the arc gases generated within the arc extinguishing structures during the extinguishing of the arc.

Group assemblage B is very similar to group assemblage A except that the two insulating plates 2'7 are assembled on opposite sides of a secondary assemblage; this secondary assemblage, which is a capacitance unit, comprises a mica plate 25 having the common slots .34 and 35, as shown in Fig. 9, assembled between two magnetic plates 32, each lined with an insulating plate 26 (Fig. 10). The plurality of insulating plates 28 is common of both of the group assemblages.

In this modification of my invention, I also employ the previously mentioned graphite impregnated fullerboard d'scs 31 for interconnecting the magnetic plates 32, and in addition, I provide a mica plate 25 in the top portion of the arc extinguishing structure for the purpose of strengtheningthe insulation adjacent the point whe e the circuit is closed. However, since the openings 29 do not exist in the mica plates 25 and since it is necessary to provide a continuous admit tance path between the interconnected magnetic plates and the arcing horn 22, it is necessary to insert a special condenser unit in the top portion of the stack. This unit has been designated by the letter M, and consists essentially, of two iron plates 32 assembled on opposite sides of the mica plate 25 to form the condenser unit, and an insulating plate 2'7 having the graphite discs 31 therein. These discs connect the top iron plate 32 with the arcing horn 22 and complete the admittance pathto the line terminal 18.

The first element of the complete assemblage of the modified arc-extinguishing structure shown in Fig. 14 is the top insulating plate 21, as shown in Fig. 9. This plate is provided with an arcing horn 22 and the slot 35 which permits the passage of the contact tip 9. The special dielectric improving group M is positioned below the top plate. A plurality of group assemblages A and B, alternately disposed are next, and the final element is the bottom insulating plate 33 which has the common slot 35, the flared opening 23, the conducting plate 38, and the sliding contact 40, as shown in Figs. 2 and 12. As previously pointed out, the common slots 34 and 35 and the recesses 36 are aligned during the assemblage of the various plate elements, and the resultant modified structure is likewise a chamber having a groove or passage-formed by the slot 35 wherein the contact clips move (and wherein the arc is drawn), insulating magnetic plates arranged transverse to the arc path, vents along said grooves which are formed by the flared openings 23, and an extension of this groove into the structure, which is formed by the recesses 36 along the slots 34. The cross sectional view of Fig. 3 shows the relative positions of various plates and the arrangement of the slots.

The second modification of my invention, which is shown in Fig. 15, is essentially very similar to the modification shown in Fig. 14. That is, this modification has the same top plate 21, the same dielectric improved element M, the same alternately disposed group assemblages A and B, and the bottom plate 33 which is common to all modifications of the device. In this modification, however, the different group assemblages in the different portions of the stack have difierent electrical characteristics, that is, the thickness of the mica plates 25 used in forming the condenser units increases progressively as the bottom of the stack is approached. Similarly, the diameter of the graphite impregnated discs 31 decreases progressively as the bottom of the stack is approached. The result of this decrease in size is to efiect a grading of the admittance path in various portions of the stack. The maximum capacitance and the maximum conductivity are concentrated in that portion of the stack where the voltage gradient is normally the largestassuming like dielectric and like conducting material. The gradations shown in Fig. 15 are somewhat exaggerated, but it is believed that this exaggerated showing more clearly illustrates this feature of my invention which is of particular importance in high voltage applications.

The operation of my invention may best be discussed in conjunction with Figs. 16, 17, and 18 and the curve of Fig. 19; Fig. 16 shows diagrammatically, the electrical characteristics of a circuit breaker having the previously described type of arc extinguishers. For the purposes of this discussion, it has been assumed the right-hand terminal of the interrupter is above ground potential, and that the left-hand terminal of the interrupter is substantially the same amount below the ground potential. The condensers C1 and C2 have been substituted for the total distributed capacity of the right-hand stack to the tank, and the capacitances ca and C4 have been substituted for the total distributed capacity of the left-hand stack in the tank; both of the distributed capacities, in reality, result from the summation of increments of capacity along the entire length of each of the stacks. Similarly, the condensers C5, C6, C1, C8, C9, and C10 have been substituted for the internal capacity of the stacks proper. And the capacitances C11 and C12, and C13 have been substituted for the total stack to bridging bar capacitances and bridging bar to tank capacitance, respectively.

These capacities all result from the electrostatically floating magnetic plates which are spaced throughout the arc extinguishing structure.

The total charging current which flows on open circuit, due to the line potential, is represented by I. The current in the top of the right-hand stack is represented by 5 and current in the bottom of the stack is represented by in. The leakage currents from the right-hand stack to the tank are represented by 11 and 2. The corresponding currents in the left-hand stack are is and 2'12, is, and i4 respectively; and the current from the bridging bar to the tank is represented by in. It is evident, therefore, that the charging current is in the upper portion of the righthand stack will be equal to the current in at the lower end plus the stack leakage currents i1 and i2 which flow from the stack to the tank. Likewise, the current is in the top of the left-hand stack will be made up of the current 2'12 that fiows intothe bottom of the stack plus the currents i3 and 211 which fiow from the tank to the stack. From this simplified analysis, it follows that, with the potential applied as indicated, the current through each element of each of the stacks will increase as the terminal 115,

or upper end of that stack is approached. The impedance of the stack to this fiow of current is spread substantially uniformly over the entire length of the stack, and may be considered as dz per elemental length; the elemental voltage drop stack is determined at any particular point by 5 the magnitude of the current which fiows through the stack at that point. If the impedance of the stack is high in comparison with the impedance of the space between the stack and the tank wall the voltage gradient in the upper portions of the stack will reach the maximum possible value. If, however, the impedance of the stack is low in comparison with the impedance of the space between the stack and the tank, practically all of the leakage current will fiow entirely through the stack, and the result will be an intensifying of the voltage gradient at the lower portions of the. structure. These two extreme variations are illustrated diagrammatically in Figs. 17 and 18; the distribution of the charging currents being indicated by the position and number of the arrows. The best operating condition is somewhere between these two extremes, and may be obtained, as I have pointed out, by the introduction of a moderate value of admittance between the electrostatically floating conducting plates.

The magnitude of the admittance to be inserted within the stack structure to give its impedance the correct value depends upon a numher of variables, such as the mechanical dimenvoltage gradient along'said plates.

2. In an arc extinguishing device, a plurality of spaced plates of conducting material positioned along the arc path, each of said plates being insulated from the adjacent plates and from the arc, and admittance means for controlling the voltage gradient along said plates, said admittance means including said plates of conducting material and means for electrically connecting some of said plates.

3. In an arc extinguishing device, a plurality of spaced plates of conducting material positioned along the arc path, at least some of said plates being 01 magnetic material for moving the arc, each of said plates being insulated from the adjacent plates, means for preventing the are from contacting said plates during the operation of said device, and admittance means for connecting some of said plates to decrease the normal impedance therebetween.

4. In an arc extinguishing device, a plurality of plates of conducting material, at least some of which are of magnetic material for moving the arc, means of insulating materialhaving openings therein for spacing said plates of conducting material, and conducting means positioned in some of said openings for electrically connecting some of said plates of conducting material and thereby controlling the distribution of leakage currents within said device.

5. In an arc extinguishing structure, a plurality of spaced plates of magnetic material positioned substantially transverse to the arc path for moving the are, means for-insulating each of said na es from the adjacent plates of magnetic material and from the arc, and admittance means for electrically connecting some of said plates of magnetic material, thereby controlling the voltage gradient along said structure.

6. In an arc extinguishing structure, a chamber, partly of insulating material, having a grooved opening therein, means for establishing the are within said opening, plates of magnetic material positioned substantially transverse to the arc path for moving the arc'into said chamber, means for insulating said plates from the arc, and conducting means which interconnect some of said plates of magnetic material to provide a conducting path through said chamber.

'7. In a circuit interrupter, separable contact members for opening and closing the circuit, a body .of liquid, and an arc extinguishing device, said device including a chamber wherein the arc is established, and admittance means, including a plurality of serially connected resistances imbedded in the walls of said chamber, for controlling the distribution of potential. along said chamber.

8. In a circuit interrupter,-separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a chamber wherein the arc is drawn, a plurality of spaced plates of conductmagnetic material throughout the structure.

ing material, at least some of which are of magnetic material for moving the arc in said chamber and means for electrically connecting some of said plates, said connected conducting plates forming a plurality of serially connected capacitances which provide an admittance path for controlling the distribution of potential along said chamber.

9. In 'a circuit-interrupter, separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a chamber, at least partly of insulating material, wherein the arc is drawn, a plurality of conducting plates positioned adjacent the arc path, at least some of said plates being of magnetic material for moving the arc in said chamber, insulating means having a passage therethrough for spacing some of said conducting plates, means for insulating said,plates from the are at all times, and conducting means Q which extend through said passages in said spacing means for electrically connecting some of said conducting plates, said plates and said conducting means forming an admittance path for controlling the distribution or potential along said chamber. r

10. In a circuit interrupter, separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, 165 said device including a chamber, partly of insulating material, wherein the arc is drawn, a plurality of superposed, spaced plates of conducting material, at least some of which are of magnetic material for moving the arc in said chamber, spacing means for said conducting plates including a plurality of plates of insulating material having openingstherein', said openings aligning to form a passage between some of said superposed conducting plates, and conducting means positioned in said passages for interconnecting some of said conducting plates.

, 11. In a circuit interrupter separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a plurality of groups of plates, each group ofwhich includes a pair of plates of insulating material having slots therein, a plate of magnetic material, having a slot therein, which is interposed between said insu-' lating plates, and a plurality of plates of insulating material having slots therein and recesses along said slots, said slotsin all of said plates being aligned to form a groove in which said are is drawn, said groove having vent openings lon- 'gitudinally along said arc path, some of said insulating plates having additional aligned openings containing conducting means of high resistance material for interconnecting the plates 'of 12. In a circuit interrupter, switching means/ including a movable bridging means of conducting material, for securing a plurality of serially connected breaks in the controlled circuit, are extinguishing, means for each of'said breaks, and 1 impedance means fo'r'controlling thedivision of voltage betwee'msaid serially. connected breaks, at least during a portion of the operation of said interrupter, said impedance means providing a conducting path between the. controlled circuit 1 5 and said bridging .means. 13. In a circuit interrupter, switching means i'or securing. a plurality of serially connected breaks in the'controll circuit, are extinguishing means for each, 01' sai breaks, said switching 15:1

sions of the apparatus, the dielectric used, the circuit voltage, and others; in fact, the complexness of the problem has necessitated a trial and error solution. For each structure, suflicient data are obtained to draw a curve as shown in Fig. 19, which shows the variation of stack fiashover voltage with stack impedance and, since high stack fiashover voltage is the criterion for most efiicient operation, a ready selection of the proper size admittance elements, for the particular structure involved, may be made.

Considering the effect of varying. the stack impedance, it can be seen from the curve that the fiashover voltage will have a maximum point at some intermediate value of impedance. If the value of the stack impedance is relatively low, the fiashover value of the stack will be correspondingly low. As the stack resistance is increased, the fiashover voltage will increase until a point is reached where further increase in stack resistance causes such an increase in the leakage current flowing between the stack proper and the metal tank and breaker parts that breakdown results from the excessive voltage gradient at the top of the stack. It is desirable, therefore, that the overall impedance of the stack (as shown in Fig. 16) be adjusted to some value between the points A and B and as near to the maximum fiashover as possible.

Curves similar to Fig. 19 may be drawn for the resistance-condenser structures of Figs. 14 and 15 and other modified structures. Furthermore, this method permits the most eflicient operation of stack structures which have different dielectrics in difierent parts of the structure.

Figs. 17 and 18, as mentioned above, show the effects of high and low overall stack resistance on the electrostatic field distribution within the circuit breaker. If the impedance is considerably greater than that shown by the point B on the curve, a field distribution such as the Fig. 17 results. The leakage currents and the corona forming voltage gradients are then concentrated in the top portion of the stack, at which point flash- .over to the tank will occur. For an overall stack impedance of an appreciably lesser value than that shown by point A on the curve, the field distribution is approximately that shown in Fig. 18. Here, the leakage currents are concentrated in the lower portions of the stack and thefiashover to the tank will occur at that point. The ideal field distribution is, of course, somewhere similar between these two extremes. I have not attempted to apply quantitative values during this discussion, because any specific values would apply only to some one particular structure.

It often happens during the operation, or during the testing, of high voltage circuit breakers that it is desirable to ground one terminal of a circuit breaker while line potential is impressed on the other terminal. This condition creates a new problem, in that a large percentage of the total difierences of potential may be confined to one of the arc extinguishing structures. Referring to Fig. 16, it will be seen that if the lefthand terminal is grounded and if the admittance path provided by the ca'pacitances C1, C2, and C13 is large in comparison with the admittance path through the arc extinguishing structures provided by the capacitances C5, Cs,C1, C11, C12, C10. C9, and C8, the division of voltage between the two are extinguishing structures at the time current zero must be very unequal, as a result of the unequality of the distribution of the charging currents. In fact, tests would indicate that for some apparatus as much as 90% of the total applied voltage may be concentrated across one of the arc extinguishers. This unequal distribution of voltage is very undesirable both because of the dangerous potential stresses set up and because of the accompanying reduction in breaker efiiciency. My invention, however, by providing an admittance path through the arc extinguishing structures, which path is conductively connected at the lower .end of each structure to the bridging bar, assures a substantially equal division of voltage at all times--the bridging bar being positioned, electrostatically midway between line and ground.

. Thus, the embodying of my invention into an arc extinguishing device not only does not interfere with but actually improves the normal functionlng of that structure. The are is drawn within the groove formed by the aligned slots 35, and is almost instantly forced, by the magnetic action of the slotted iron plates 32, into the narrower connecting slots 34 and the connecting recesses 36 within the structure; at the same time, the arc transfers from the stationary contact member to the arcing horn 22. Gases are formed within the chamber, and, in venting, these gases flow outwardly through the arc in a transverse direction, thereby cooling and deionizing it. This outfiowing gas also assists in building up the dielectric strength of the arc path after the current has reached its zero value.

By properly adjusting the stack impedance,

the restored voltage tending to break down the arc space can be prevented from building up across the arc terminals at a too rapid rate, and from reaching too high a value. Also by the use of the previously described means for connecting the bridging bar to the lower end of the serially connected conducting plates within the arc extinguisher, the controlled circuit potential can be made to divide itself equally between the two breaks. Furthermore, my invention permits the strengthening of the dielectric adjacent to the point of contact. In connection with this last, it is important to note that prior to my discovery any attempt to improve the dielectric in portions. of the structure resulted in very objectionable and very dangerous local increases in the voltage gradient.

Attention is directed to the fact that the impedance means associated with each of the arc extinguishing devices is disconnected from the the normal open circuit position. This arrangement prevents unreasonably large leakage currents from flowing through the device when it is in the normal open circuit position, and thereby aids in preventing improper relay operation or line'disturbances. Moreover, although the impedance means is disconnected from the bridg-' ing member when the switch is in the normal open circuit position, it is still efiective to control the distribution of such leakage currents as may flow through the arc extinguishing stack structures when the breaker is in the open position.

While I have disclosed how my invention might be applied to one particular structure, I do not wish to limit myself thereto except asset forth in the claims. The idea is broad and could be effectively applied in many ways by those skilled in the art. Also, I do not wish to confine myself to resistance or to resistance and capacitance means for constructing an .arc extinguishing structure having the operating characteristics bridging member when the circuit breaker is in means including a movable bridging means of conducting material, and impedance means associated with each of said are extinguishing means for controlling the division of voltage between said serially connected breaks, said impedance means providing a conducting path of predetermined admittance between the controlled circuit and said bridging means.

14. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit, said means including a movable bridging means of conducting material which is electrostatically isolated from the controlled circuit when the interrupter is in the fully open position, are extinguishing means for each of said breaks, and impedance means associated with each of said are extinguishing means for controlling the division of voltage between said serially connected breaks, said impedance means providing a conducting path be tween the controlled circuit and said bridging means during at least a part of the opening operation of said interrupter.

. 15. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit, an arc extinguishing device for each of said breaks, a movable bridging member of conducting material, and impedance means, which provide a conducting path between the controlled circuit and'said bridging means, for controlling the distribution of potential gradient along saidlarc' extinguishing devices and for controlling the division of potential between said serially connected breaks, said impedance means forming an integral part of said are extinguishing devices, said arc extinguishing devices having means of conducting material afiixed thereto for electrically connecting said bridging member with said impedance means.

16. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit, an arc extinguishing deice for each of said breaks, a movablebridging member of conducting material, and impedance means forming a part of each of said are extinguishing devices for controlling the distribution of potential gradient along said are extinguishing devices, and for controlling the division of potential between said serially connected breaks, each of said are extinguishing devices including a plurality of superposed, spaced plates of conducting material, positioned adjacent the path. of insulating material having a assage therethrough for spacing said plates of conducting material, conducting means positioned within said passage for interconnecting some of said plates of conducting material, and a for contacting said bridging member during the opening and closing of said interrupter.

17. In an arc extinguishing device a plurality of spaced plates of conducting material positioned along the arc path, at least some of said plates being of magnetic material for moving the arc, and each of said plates being insulated from the adjacent plates and from the arc, and admittance means graded in value along said device for controlling the potential gradient between said plates, said admittance means including at -16'1Sl7 some of said plates of conducting material and means for electrically connecting some of said plates.

3.8. I- an arc extinguishing structure, separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a chamber wherein the arc is drawn, a plurality of spaced plates of conducting material, at least some of said plates being of magnetic material for moving the arc in said chamber, and means for interconnecting some of said plates, said interconnected conducting plates forming a plurality of serially connected capacitances which are graded in value along said chamber, said graded capacitances providing an admittance path for controlling the distribution of potential along said chamber.

19. In a circuit interrupter, separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a chamber, partly of insulating material, wherein the arc is drawn, a plurality of superposed, spaced plates of conducting material, at least some of said plates being of magnetic material for moving the arc in said passage, spacing means for said conducting plates including a plurality of plates of insulating material having openings therein, said openings aligning to form a passage between adjacent conducting plates, resistance means, graded in value along said chamber, positioned in said passages which means interconnect some of said conducting plates.

20. In an arc extinguishing device, a plurality of plates of conducting material, means of insulating material having openings therein for spacing said plates of conducting material, and conducting means of graphite impregnated fullerboard positioned in some of said openings for electrically connecting some of said plates of conducting material and thereby controlling the distribution of leakage currents within said device.

21. In a circuit interrupter, separable contact members for opening and closing the circuit, a body of liquid, and an arc extinguishing device, said device including a chamber wherein the arc is established, a plurality of spaced plates of conducting material, and means of graphite impregnated fullerboard for electrically connecting some of said plates, said conducting plates forming a plurality of serially connected capacitances which provide an admittance path for controlling the distribution of potential along said chamber.

22. In a circuit interrupter, separable contact members for opening and. closing the cir cuit, a body of liquid, and an arc extinguishing device, said device including a chamber, partly of insulating material. wherein the arc is drawn, a plurality of superposed, spaced plates of conducting material, spacing means for said conducting plates including a plurality of plates of insulating material having openings therein, said openings aligning to form a passage between adjacent conducting plates, and inserts of graphite impre nated fullerboard positioned in some of the ali ning openings in said plates for interconnecting some of said conducting plates.

23. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit. said switchin means includ ng a movable bridging member of conducting material. impedance means including a plurality of serially connected, graphite impreenated fullerboard resistance elements, for cont olling the division of voltage between said serially connected breaks, and contact means, electrically connected to said impedance means, which engages said bridging member during at least a part of the opening and closing operation of said interrupter, said impedance means providing a conducting path between the controlled circuit and said bridging member.

24. In a circuit interrupter; switching means for securing a plurality of serially connected breaks in the controlled circuit, said switching means includinga movable .bridging member of conducting material; an arc extinguishing device for each of said serially connected breaks, each of said are extinguishing devices having a passage therein which is insulated from the are; impedance means, including a plurality of serially connected, graphite impregnated resistance elements, which are positioned in said passage, for controlling the division of voltage between said serially connected breaks, and contact means electrically connected to said impedance means, which engages said bridging member during at least a part of the opening and closing opera tion of said interrupter, said impedance means providing a conducting path between the controlled circuit and said bridging member.

25. In a circuit interrupter; switching means for securing a plurality of serially connected breaks in the controlled circuit, said switching means including a movable bridging member of conducting materialyan arc extinguishing device for each of said serially connected breaks, each of said are extinguishing devices including a plurality of superposed, spaced plates of conducting material, spacing means for said conducting plates comprising means of insulating material having openings therein, and impedance means comprising a plurality of serially connected graphite impregnated resistance elements, which are. positioned in said openings, for interconnecting some of said conducting plates; and contact means electrically connected to said impedance means which engages said bridging member during at least a part of the opening and closing operation of said interrupter; said impedance means controlling the voltage gradient along each of said are extinguishers, and, in combination with saidcontact means, providing aconducting path between the controlled circuit and said bridging member,-thereby controlling the division of voltage between said serially connected breaks.

26. In a circuit interrupter, separable contacts for opening the circuit, and an arc extinguishing structure comprising a. chamber formed by the assembly of a plurality of groups of plates, each group including a pair of plates of insulating material having slots therein, a plate of magnetic material having a slot therein interposed between said insulating plates, and a plurality of plates of absorbent material having slots therein and recesses along said slots, said slots all being aligned to form a groove which extends longitudinally along said structure and within which said are is drawn, some of said insulating and said absorbent plates having additional alignedopenings therein, said additional openings containing inserts of conducting material, said inserts interconnecting some of said plates of magnetic materialthroughout the structure.

27. In a circuit interrupter, a body of liquid, separable contact members for establishing an arc in said liquid, and an arc extinguishing struc ture including a plurality of groups of plates, each group including a pair of plates of insulating material having slots therein, a plate of magnetic material, having a slot therein, interposed between saidinsulating plates, an insulating strip positioned between said insulating plates for protecting the inner edges of said magnetic plate from the are, a plurality of plates of insulating material having slots therein and recesses along said slots, said slots all being aligned to form a groove in which said are is drawn, some of said insulating. plates having additional aligned openings therein, said additional openings containing conducting plates of graphite impregnated fullerboard which conducting plates interconnect some of the plates of magnetic material throughout the structure.

28. In a circuit interrupter, a body of liquid, a separablecontact member for establishing an. arc in said liquid, and an arc extinguishing structure, including a plurality of groups of plates, each group including a pair of plates of insulat ing material having slots therein, a plate of magnetic material having a slot therein interposed between said insulating plates, an insulating strip positioned between said insulating plates for protecting the edge of said magnetic plate from thearc, a. plurality of plates of absorbent material having slots therein and recesses'along said slots, said. slots all being aligned to form a. vented longitudinal-passage in which said are is-dra-wn,v some of said insulating and said absorbent plates having additional aligned openings therein, said additional openings containing conducting plates of graphite impregnated fullerboard which conducting plates interconnect some or the plates of magnetic materialthroughout the structure.

29. In a circuit interrupter, a body of liquid, separable contact members for establishing an arc in said liquid, and an arc extinguishing structure including a plurality of groups of plates each of which groups includes a pair of plates of insulating material having slots therein, a plate of magnetic material having aslot therein interposed between said insulating plates, aminsulating strip positioned between said insulating plates for protecting the inner edges of said magnetic plate fromthe arc, and a plurality of plates of insulating material having slots therein and recesses along said slots, said slots all being aligned to form a groove in which said are is drawn, all of said insulating plates in some groups having additional aligned openings therein, said openings containing conducting plates of graphite impregnated fullerboard, which conducting plates interconnect some of the plates of magnetic material throughout the structure, said structure having in some of the remaining groups additional insulating means interposed between two plates of conducting material for altering the admittance characteristics of those groups.

30. In a circuit interrupter, means at least partially of insulating material for defining a passage, means for drawing an arc in said passage, means comprising a plurality of members or" magnetic material for moving the arc in said passage, said members being insulated from the arc, and means for electrically interconnecting at least some of said members of magnetic material to control the voltage gradient therebetween,

31. In a circuit interrupter, means at least partially of insulating material for defining a passage, means for drawing an arc in said passage, means for moving said are in said passage comprising a plurality of spaced members of magnetic material disposed along said passage for moving the arc thereon, means for insulating said members from the arc, and means for electrically interconnecting at least some of said members to control the voltage gradient along said passage.

32. In a circuit interrupter, means of insulating material for defining the walls of a passage, means for drawing an arc in said passage, means for moving the arc in' said passage comprising members of magnetic material imbedded in said walls, said members being insulated from the arc, said walls having passageways therein between some of said members, and means of conducting material disposed in said passageways for electrically connecting some of said members to control the voltage gradient therebetween.

33. In a circuit interrupter, means of insulating material for defining the walls of a passage, means for drawing an arc in said passage, means for moving the arc in said passage comprising a plurality of spaced members of magnetic material positioned along the longitudinal axis of said passage and imbedded in said walls, said members being insulated from the are, said walls having passageways therein extending between some of said members, and means of conducting material disposed in said passageways for electrically connecting some of said members to control the voltage gradient therebetween.

34. In a circuit interrupter, means at least partially of insulating material for defining a passage, means for drawing an arc in said passage, a plurality of spaced members of conducting material positioned adjacent said passage, at least some of said members being of magnetic material for moving the arc in said passage, means for insulating said members from the arc and from each other, the spacing between some of said members being less than the spacing between the other of said members in order to provide units of increased capacitance, and means for interconnecting some of said members to control the voltage gradient along said passage.

35. In a circuit interrupter, means at least I partially of insulating material for defining a passage, means for drawing an arc in said passage, a plurality of spaced members of conducting material positioned along the longitudinal axis of said passage, at least some of said members being of magnetic material for moving the arc in said passage, means for insulating said members from each other and from the arc, some of said members being spaced closely adjacent each other in order to create capacitance units, and means for electrically connecting said capacitance units in order to control the voltage gradient along said passage.

36. In a circuit interrupter, switching means including a movable bridging means of conducting material for securing a plurality of serially connected breaks in the controlled circuit, arc extinguishing means for each'ol" said breaks, impedance means for controlling the division of voltage between said serially connected breaks, and means for connecting said impedance means to said bridging means during at least a portion of the operation of said interrupter, said connecting means being so arranged that said impedance means is disconnected from said bridging means when said interrupter is in the open circ lit position.

37. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit, an arc extinguishing device for each of said breaks, a movable bridging member o conducting material, impedance means, for controlling the division of potential between said serially connected breaks,

and means for providing a conducting path between the controlled circuit and said bridging means at least during a portion of the operation of said circuit interrupter, said connecting means being so arranged that said impedance means are disconnected from said bridging member when said interrupter is in the open circuit position, each of said are extinguishing devices including a plurality of spaced plates of conducting material which are insulated from each other and are insulated from the arc, and said impedance means being adapted to interconnect at least some or" said plates.

38. In a circuit interrupter, switching means including a movable bridging member for securing a plurality of serially connected breaks in the controlled circuit, an arc extinguishing device for each of said breaks, and impedance means, forming a part of each of said arc extinguishing devices, for controlling the division of potential between said serially connected breaks, each of said are extinguishing devices including means for defining an arc passage, a plurality of spaced plates of conducting material positioned adja cent said are passage, at least some of said plates being of magnetic material for moving the are within said arc passage, and means for contacting said bridging member during at least a portion of the opening and closing operation of said interrupter in order to connect said impedance means therewith, said connecting means being so arranged that said bridging member is disconnected from said impedance means when said interrupter is in the open circuit position.

39. In a circuit interrupter, switching means including a movable bridging member of conducting material, for securing a plurality of serially connected breaks in the controlled circuit, an arc extinguishing device for each of said breaks impedance means which provides a conducting path between the controlled circuit and said bridging member for controlling the flow of leakage currents through and along said are extinguishing devices, and means for connecting said impedance means with said bridging member during at 1 least a portion of the operation of said interrupter in order to secure an equal division of potential between the serially connected breaks, said connecting means causing said impedance means to be disconnected from said bridging 125 member when said interrupter is in the open circuit position.

40. In a circuit interrupter, switching means for securing a plurality of serially connected breaks in the controlled circuit, an are ex- 130 tinguishing device for each of said brealns, which device includes means, at least partially of insulating material, for defining an arc passage, means comprising a plurality of spaced members of magnetic material for moving the arc' Within 135 said passage, means for insulatingsaid members of magnetic material from each other and from the arc, impedance means for controlling the flow of leakage currents through each of the are ex- .tinguishing devices in order to efiect equal dis- 140 tribution of potential between said serially connected breaks during operation of said interrupter, and means for connecting said impedance means with said bridging member, said connecting means being so arranged that said impedance 145 means is disconnected from said bridging means when said interrupter is in the open circuit position.

BENJAMIN P. BAKER. 

